The invention relates to a device for laterally shifting a towed assembly with respect to the trajectory of a towing vehicle.
More particularly, the invention concerns a device associated to an assembly towed from a ship and adapted to laterally shift the assembly with respect to the ship route.
The device according to the invention may be used for example to laterally shift, with respect to a towing ship, an assembly of seismic equipments such as seismic sources or receivers.
In order to laterally shift an object with respect to the trajectory of a towing ship for example, there can be used for example a device such as that described in the French Pat. No. 2 296 562. This device comprises a frame secured to floats navigating at the surface. Under the floats are secured submerged deflection means formed of a plurality of paddles arranged parallelly to one another. The transported load is secured under the device through a cable and is towed under water. The disadvantages of this type of device result from its sensitivity to the disturbing action of the waves and from the speed variations of the towing ship having the effect of varying the position of the cable holding the load and accordingly of varying the immersion depth thereof, this being a disadvantage in certain applications in the field of marine seismic prospecting, for example.
The lateral shift of a submerged object may also be obtained by one or more plates or "panels" towed under water and secured to the end of a towing cable, so that the hydrodynamic forces have a transversed component which laterally shifts the same with respect to the ship route. These panels are formed in most cases of mere plates slightly rounded and provided on their concave face with strengthening ribs and several elements for securing the traction cables. These panels are mainly used to widen the opening of the fishing nets. The disadvantage of these devices results from their substantial drag which generates parasitic vibrations. When such panels are used for example to shift an assembly of submerged seismic sensors with respect to the trajectory of a towing ship, the parasitic vibrations generated by the displacement of these panels are superimposed on the seismic signals sensed by the receivers, in response to impulses generated by a seismic source also towed from the ship, and reflected by the different subsoil layers, and disturb the recording of these signals.